Limit switch operating mechanism

ABSTRACT

A limit switch operating head subassembly mountable at its mating surface onto a switch subassembly in any one of a number of different angular positions and may be detached without any parts falling out. The operating head subassembly has an operating arm pivotable in opposite directions for switch actuation. This operating arm is secured to a shaft that operates cams, rockers and slide members to operate an actuating plunger through a presettable mechanism allowing by-pass in one direction. The slide members are internally compression spring biased threaded members allowing stepless length adjustment. The presettable by-pass mechanism has a flanged plunger on a square pin and a notch in the flange to allow presetting the plunger notch at 90* intervals for switch operation in both directions or by-pass in one direction of operating arm movement. The operating shaft has a seal design that enhances sealing effect under fluid pressure and is smaller so as to use less material. An adjustable coupling mechanism transmits the plunger motion to the contact actuator. The stepless length adjustment of the slide members and the adjustment of the coupling mechanism afford adjustment of the plunger motion relative to the mating faces of the operating head and switch subassemblies, respectively, to afford presetting of switch tripping at five degrees of arm movement.

United States Patent [1 1 Duncan et al.

[ LIMIT SWITCH OPERATING MECHANISM [75] Inventors: Eugene F. Duncan; Robert Pearson,

both of Milwaukee, Wis.

[73] Assignee: Cutler-Hammer, Inc., Milwaukee,

Wis.

[22] Filed: Feb. 26, 1973 [21] Appl. No.: 335,905

Primary ExaminerHerman J. Hohauser [57] ABSTRACT A limit switch operating head subassembly mountable at its mating surface onto a switch subassembly in any one of a number of different angular positions and may be detached without any parts falling out. The

[ 51 Feb. 19, 1974 operating head subassembly has an operating arm pivotable in opposite directions for switch actuation. This operating arm is secured to a shaft that operates cams, rockers and slide members to operate an actuating plunger through a presettable mechanism allowing by-pass in one direction. The slide members are internally compression spring biased threaded members allowing stepless length adjustment. The presettable bypass mechanism has a flanged plunger on a square pin and a notch in the flange to allow presetting the plunger notch at 90 intervals for switch operation in both directions or by-pass in one direction of operating arm movement. The operating shaft has a seal design that enhances sealing effect under fluid pressure and is smaller so as to use less material. An adjustable coupling mechanism transmits the plunger motion to the contact actuator. The stepless length adjustment of the slide members and the adjustment of the coupling mechanism afford adjustment of the plunger motion relative to the mating faces of the operating head and switch subassemblies, respectively, to afford presetting of switch tripping at five degrees of arm movement.

PATENIEUFEB 1919M 3. 7 93 ,492

Q SHEET? Hi2 I LIMIT SWITCH OPERATING MECHANISM BACKGROUND OF THE INVENTION Limit switch operating mechanisms have been known heretofore. However, prior mechanisms have had one or more of the disadvantages such as loose parts that might fall out when the operating head is removed, requirement of a special tool or inconvenient or subject to error in presetting for by-pass in one direction, difficult to adjust the switch tripping point, external buttons or parts subject to jamming by paint or the like, or presetting parts that might come loose during use, operating shaft seal ineffective or subject to failure, and the like.

The present invention provides a limit switch operating mechanism that overcomes such disadvantages.

SUMMARY OF THE INVENTION This invention relates to limit switch operating mechanisms and more particularly to operating mechanisms wherein the operating head is a unitary subassembly and includes means facilitating presetting for by-pass in one direction of operating arm movement and adjusting the switch actuator plunger for a given trip point.

An object of the invention is to provide an improved limit switch operating mechanism.

A more specific object of the invention is to provide an improved limit switch operating head subassembly that is removable from the switch contact subassembly without any parts falling out.

Another specific object of the invention is to provide an improved limit switch operating head that facilitates presetting to by-pass in one direction of operating arm movement upon removal of the operating head and without the use of any special tool or the like.

Another specific object of the invention is to provide an improved limit switch operating head that facilitates easy adjustment of the switch-actuating plunger movement to attain switch tripping at a given operating arm angle.

A further specific object of the invention is to provide an improved limit switch operating head that affords stepless adjustment of its switch-tripping plunger movement relative to its mounting surface.

Other objects and advantages of the invention will hereinafter appear.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view of a limit switch partly in section to show the adjustable coupling means whereby force is transmitted from the operating head to the contact actuator;

FIG. 2 is an enlarged cross sectional view taken along line 22 of FIG. 1;

FIG. 3 is a left side view of the operating head subassembly of FIG. 2 showing the mating face thereof and the operating shaft bushing being shown in crosssection to show the shaft seal;

FIG. 4 is an enlarged fragmentary view of the upper cross-section of the seal of FIG. 3;

FIG. 5 is a cross-sectional view taken along line 55 of FIG. 2 showing the cams, rockers and slide members and FIG. 6 is an enlarged cross-sectional view taken along line 6-6 of FIG. 1 showing the mating face of the contact subassembly and the adjustable coupling means mounted therein.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown a limit switch according to the invention. This limit switch comprises an operating head subassembly 2 and a switch subassembly 4. These two subassemblies are self-enclosed and are constructed so that the operating head subassembly may be detached without any parts falling out. The operating head subassembly is held on the switch subassembly by four screws 6, one at each corner, and may be separated therefrom at its mating surface when the screws are removed. The operating head subassembly may be detached in order to set it at any desired 90 angle realtive to the mounting surface of the switch subassembly which is at the bottom as seen in FIG. 1.

The operating head subassembly is provided with an operating arm 8 having a roller 8a at its swingable end for engagement by a moving machine part or the like that actuates the switch. This operating arm may be mounted at any desired stepless angle onto shaft 10 and secured thereon by tightening screw 8b. For this purpose, the apertured end of arm 8 if split and has a metal strap wrapped around this split end portion to pinch the arm on the shaft when the screw is tightened.

Housing 2a of the operating head subassembly is provided with a short integral hub or bushing 2b for supporting a shaft seal as hereinafter more fully described in connection with FIGS. 3 and 4.

Switch subassembly 4 is comprised of two parts including a contact enclosing part 4a that extends along the top thereof toward the right and then down as shown in FIG. 1 and a connector enclosing part 4b that fills the space below the contact enclosing part. The contact enclosing part houses the switch contacts, the contact actuator 12 whose right-hand end is visible in FIG. 1, and the adjustable coupling mechanism 14 within its downwardly extending right-hand end portion whereby the contact trip point may be readily adjusted when the operating head is removed. This righthand end portion provides a mating surface to which the operating head is joined. The connector enclosing part houses electrical connector sockets into which electrical plugs of the contact enclosing part are plugged and is provided with an opening at its left-hand end to which an electrical conduit, enclosing. conductors, is attached. Parts 4a and 4b are secured to one another by a pair of screws 16 and are sealed by a rubber gasket 18 therebetween. The connector enclosing part is normally mounted onto a stationary machine part or the like, being provided with a pair of slots and screw holes for this purpose, and the contact enclosing part 4a with operating head 2 attached thereto is then secured to the mounted part 4b.

The operating head encloses an operating mechanism as shown in FIGS. 2-6. Shaft 10 extends through a first sleeve bearing 20 as shown in FIG. 2, then through a first cam 22 and a second cam 24 shown in FIG. 5 and into a second sleeve bearing 26 shown in FIG. 3. Shaft 10 is held in the housing by a C-retainer snapped into an annular groove in the shaft between cam 24 and sleeve bearing 26. The two cams are provided with integral bushings extending into abutting relation with one another, bushing 22a being shown in FIG. 2. A wound helical return spring 28 surrounds these cam bushings and has its opposite ends hooked on the respective cams to bias the crank shaft into its center off "position. One end of this spring is hooked into notch 22b shown in FIG. 2 to bias projection 22c of cam 22 against a stop formed by rocker mounting shaft 30.

In order for the cam to move the shaft to center off position, the shaft is provided with a flat portion a and the cam is provided with an internal nib 22d that bears against the lower side of this flat portion. The spring biases cam 22 counterclockwise in FIG. 2 and the cam rotates shaft 10 counterclockwise to its center off position shown in FIG. 2.

In a similar manner, the return spring biases cam 24 clockwise against the opposite side of stop shaft 30 and the internal nib of this cam bears against the upper side of flat portion 10a of the shaft.

Thus, the shaft is biased into its center off position and can be turned in either direction against the force of the return spring. As seen in FIG. 2, the shaft can be turned counterclockwise until the upper side of flat portion 10a abuts nib 22d. In a similar manner, the shaft can be turned clockwise until the lower side of flat portion 10a abuts a like nib within the bore of cam 24. Clockwise movement of the shaft rotates cam 22 to rock rocker 32 clockwise. Counterclockwise movement of the shaft rotates cam 24 to rock rocker 34 counterclockwise. Rockers 32 and 34 are pivoted on shaft 30 and serve to lift slide members 36 and 38 when the cam supporting shaft is rotated in opposite directions, clockwise and counterclockwise, respectively.

Since the two slide levers are similar, slide member 36 will be described in detail. As shown in FIGS. 2 and 3, this slide lever is provided with a flat-headed screw 40 whose shank 40a extends through a push plate 42, diaphragm seal 44, a bushing 46, a helical compression spring 48 and a nut 50 which is threaded on its end. As will be apparent, spring 48 biases push plate 42 against the head of the screw so that when rocker 32 is rocked clockwise to engage nut 50 and push the slide member in the left-hand direction in FIG. 2, the push plate will move with it and actuate plunger 52 by sliding it to the left on pin 54.

As shown in FIG. 3, push plate 42 is provided with a central lifting tongue 42a for listing plunger 52 by its flange 52a, and a pair of side tongues 42b for preventing the plunger from falling off its pin. For this purpose, center tongue 42a extends straight under the flange of the plunger whereas side tongues 42b are offset as shown in FIG. 2 to extend over the flange.

Pin 54 is rigidly secured to the operating head housing 2. For this purpose, pin 54 is provided with an integral disc 54a at one end whereby it is welded to a metal plate 56 shown in FIGS. 2 and 3. Diaphragm seal or gasket 44 is secured to the back of this metal plate and is provided with an integral O-ring 44a embracing the peripheral edges of this plate for compression between the mating faces of the operating head and switch subassemblies. This metal plate is provided with two large apertures 56a over which the gasket extends. This gasket is provided with small holes centrally of these apertures through which the adjusting screws of slide levers 36 and 38 extend. The gasket surrounding these holes is clamped between the bushing the push plate to form a seal. Also, the gasket is formed with circular undulations within the apertures of plate 56 to afford freedom of movement for the slide members as shown in FIG. 2.

Plate 56 is secured in the operating head. For this purpose, plate 56 is provided with four peripheral fingers 56b that fit into respective notches 2c in the operating head housing. One edge of these notches is staked as indicated at 2d in FIG. 3 to secure plate 56 to the housing. In this manner, all the parts are secured so that no parts fall out when the operating head is removed from the switch subassembly. Four notches 2e are provided in the mating face of the operating head housing for registering with a pair of lugs on the mating face of the switch subassembly in the different angular positions.

Pin 54 is provided with a polygonal such as a square cross-section 54a extending up from its disc about halfway and then a round cross-section the rest of the way to its end as shown in FIGS. 2 and 3. Plunger 52 is provided with a polygonal such as a square bore to fit the square section of the pin. This permits the plunger to be lifted up on the pin and rotated to any of four spaced apart angles to present the switch for by-pass in one direction or switch operation in both directions of operating arm rotation. For this purpose, plunger 52 is provided with a flange 52a having a cutout or notch 52b as shown in FIG. 3. This notch may be positioned as shown in FIG. 3 to clear tongue 42a for by-pass in one direction. If this plunger is rotated 90 in either direction, both tongues will left the plunger for switch operation in both directions of operating arm movement. If this plunger is rotated to cause the notch to clear the center tongue in the other push plate, it will be preset for by-pass in the other direction of operating arm rotation.

The distance that plunger 52 moves in response to full operating rotation of the operating arm may be adjusted by turning screw 40 in slide member 36 and the similar screw in slide member 38 to adjust the effective length thereof. This screw becomes-accessible for turning when the operating head subassembly is removed from the switch subassembly. As shown in FIGS. 2 and 5, bushing 46 and nut 50 have wings on them whereby they are retained in pockets in the housing for linear sliding movement. Thus, the nut is held so that turning screw 40 in one direction or the other either shortens or lengthens the slide member steplessly. This affords accurate adjustment of the movement of plunger 52.

- Typically, this plunger moves its operating distance on 5 movement of the operating arm in either direction. The remainder of the operating arm movement up to its limit of about 90 is overtravel allowance.

Shaft 10 is provided with a seal to prevent the entry of fluid or dirt through bushing 2b. As shown in FIG. 3 and in the enlarged fragmentary view in FIG. 4, shaft 10 is provided with an annular groove 10b within the end of bushing 2b of the housing. This annular groove is symmetrical in having a slightly curved botton or a bottom of large radius or curvature. The left and right sides of this groove are more curved or have like, smaller radii of curvature. The end of bushing 2b has two annular shoulders, a first shoulder 2f for the annular bead of a seal 58 and a second shoulder 2g of larger diameter for a retaining washer 59. As shown in FIG. 4, shoulder 23 is ofi'set toward the end of the bushing from shoulder 2f to provide space between shoulder 2f and the washer for compression of the head of the seal. The end of bushing 2b is upset to retain washer 59.

Seal 58 is designed to utilize a very small amount of material but nevertheless to provide an effective seal against fluids and dirt. This design that uses very little material enables use of good quality material such as synthetic material made by DuPont known as Viton" which will not swell or deteriorate when subjected to certain fluids such as fire-resistant hydraulic fluids or high temperature. As shown in FIG. 4, seal 58 extends down from where its bead is pinched against shoulder 2f and then part 58a thereof extends toward the right between bearing and the shaft. At this point, part 58b of the seal turns down and toward the left and part 58c extends along the bottom of groove 10b and partly up the left side curvature of the groove. The portion 580 of the seal has a cylindrical inner wall in its relaxed state as it is formed and a diameter slightly smaller than the minimum diameter of the shaft at the center of groove 10b. Consequently, part 58c of the seal grips the shaft snugly in groove 10b, and the left and right sides of part 580 of the seal which are stretched even more by the increasing diameter of the shaft at the sides of the groove apply greater force to the shaft to afford two spaced points of higher pressure around the shaft for effective sealing. Any fluid force coming from the outside tends to spread parts 58a and 58c of the seal apart and against the bearing and shaft to enhance the sealing effect. Shaft 10 is capable of rotating within this seal as it is moved in opposite directions so that part 58c of the seal slides in the shaft groove.

The switch is provided with adjustable coupling means for coupling plunger 52 of the operating head to contact actuator 12 in the switch subassembly. This adjustable coupling means is shown in FIGS. 1 and 6 and includes a pivoting member 60 having an adjusting screw 62, and pivoted member 64. As shown in FIG. 6, pivoting member 60 is provided with a pair of laterallyextending legs 60a at its upper end that are staked into slots in the housing of contact enclosing part 4a of the switch subassembly so that its lower end is biased toward the right-hand end wall of the housing. Screw 62 is threaded laterally through the lower end portion of pivoting member 60 so that the left end of this screw abuts such end wall of the housing, there being a hard steel plate 66 between the end of this screw and the housing wall to prevent the screw from digging into the housing wall when it is turned. Thus, the screw may be turned to adjust the lower end of pivoting member 60 toward or away from the wall while the bias in the latter holds the end of the screw tight against plate 66.

Member 60 is called a pivoting member because it provides an adjustable pivot for pivoted member 64. For this purpose, the lower end of member 60 is provided with an aperture 60b at which the end of this member is bent at a right angle toward the housing wall. Thus, the strip 600 remaining between this aperture and the extreme lower end of member 60 provides a pivot for member 64. A lateral groove is provided at the left side of the lower end of member 64 at which it rests on strip 60c.

Member 64 is called a pivoted member because it is pivoted at its lower end on strip 60c and extends up wardly therefrom so that the left side of its upper end abuts the right end of contact actuator 12 as seen in FIG. 1. Screw 62 passes also through a hole in member 64 to hold it in place. This hole is oblong vertically to afford pivoted member 64 freedom of movement when actuated by plunger 52.

The portion of pivoted member 64 engaged by the end of plunger 52 is formed to provide a lateral pivot. For this purpose, member 64 is provided with a hole 64a to provide clearance for pin 54. The circular area 64b around this hole is formed with an increasing undercut both upwardly and downwardly from a horizontal center line passing through this hole as shown in FIG. 1. Thus, a lateral pivot 640 extends along this center line on both the left and right sides of hole 64a, as

shown in FIGS. 1 and 6, against which the left end of plunger 52 bears.

Thus, when the operating arm is moved to slide plunger 52 toward the left in FIG. 1, member 64 rocks counterclockwise on pivot 60c whereby the upper end of member 64 moves contact actuator 12 toward the left to trip the switch contacts.

Screw 62 affords adjustment of the trip point of the contacts. This is most conveniently done with a jig that uses the mating surface of the housing as a reference line. For example, this switch subassembly may be placed in a jig that engages the mating surface and has a projection simulating plunger 52 that is 0.305 inch long. Screw 62 is then adjusted to move the pivot 60c away from the housing wall enough to trip the switch.

Similar adjustment is then made on the operating head. The operating head is placed in a jig engaging its mating surface as a reference line. The slide member screws such as screw 40 are then adjusted so that plunger 52 extends out 0.305 inch when the operating arm is moved 5 in either direction from its center off position.

When the operating head is then attached to the switch subassembly, the contacts will trip at 5 of arm movement. For 15 arm tripping, different cams are used in the operating head.

Seal 58 hereinbefore described is effective under submersible conditions such as under six feet of water. Fluid pressure on it improves its sealing effect. It withstands seepage. On machine tools, it prevents entry of coolants and solves the leakage problem which has been a major problem in limit switches. It replaces two larger seals commonly used in the prior art. In addition to its good performance, this seal does not require extremely close tolerances of parts in manufacture. It is thin and a few thousands of an inch variation will not add excessive drag to shaft rotation. This is important on limit switches which have minimum return spring forces.

While the apparatus hereinbefore described is effectively adapted to fulfill the objects stated, it is to be understood that the invention is not intended to be confined to the particular preferred embodiment of limit switch operating mechanism disclosed, inasmuch as it is susceptible of various modifications without departing from the scope of the appended claims.

We claim:

1. A limit switch comprising:

a self-enclosed switch subassembly having an open end, and a self-enclosed operating head subassembly having a mating surface secured to said open end to close the latter and provide a limit switch allowing detachment of the operating head without any parts falling out;

said switch subassembly comprising an enclosure, switch contacts within said enclosure and switch actuating means within said enclosure and accessible at the open end thereof for actuation by said operating head;

and said operating head subassembly comprising:

a housing;

an external operating arm mounted on said housing and adapted to be moved in opposite directions to operate the switch;

a fixed guide pin having a polygonal portion extending in from one end and a round portion extending rockers mounted in said housing for actuation by said cams;

a pair of slide members in said housing for actuation by said rockers;

a flange on said plunger having a cutout at a predetermined angle;

and a pair of push plates secured to the respective slide members and extending under said flange whereby both push plates slide said plunger at said given angle and one push plate passes freely through said cutout at said different angle for bypass in one direction of operating arm movement.

4. The invention defined in claim 3, wherein:

each said slide member comprises means affording thereby to preset the switch trip point at a desired operating arm angle. 6. In a limit switch of the type having a switch housing open at one end and a switch within the housing,

switch operating means comprising:

switch actuating means in the switch housing and accessible from the open end thereof for actuating the switch;

and an operating head attached to the open end of in frOm the other end, and means mounting Said 10 the switch housing for engaging said switch actuatguide pin at said one end SO that its round end CX- ing means to operate the switch comprising; tends into the open end of said switch enclosure; 3 i h operating arm d d to b swung i OPPO- a P having a bore complementary to Said P site directions to operate the switch;

lygonal portion whereby said plunger s a pair of slide members slidably mounted in said oprotatably slidable on said guide pin to actuate said mating head for reciprocal movement; zlgrsgnz sfil le "$331132: gzgg go lzi gfi a return spring biasing said switch operating arm in its center off position from which it is ada ted to upon removal of said operating head and rotated to be swung in opposite directions; p f h 8:? to S ll between di j f means operable when said operating arm is swung in anii rzotgzl zgz s lzgng 22 58zn' gfidixg sggtive said opposite directions for moving the respective slide members; i f if g means f m a fixed guide member having a polygonal end portion p unger p051 on Sal gm 6 pm a a gwen and means mountin it to said 0 ratin head and angle for rendering said coupling means effective a round free end :Ortion gg award the to slide said plunger to cause switch operation Switch housing when said external 0 eratin arm is moved in either direction and being operable when said a plunger having bore complimieniary to Said-p0- plunger is set o n said guide pin at a different angle lygona] end portion whereby It slidably received os'd 'dm btb -rot bl lidal for rendering said coupling means effective to slide a] e f er 0 non d said plunger to cause switch operation when said ereon swltc operailon an a P to e external operating arm is moved in one direction manually shd further to sald round portion and to and for rendering said de-coupling means effective tated to angle to clear said plunger to afford by-pass when said and nieans provldmg linerfenng and non-Interfering external operating arm is moved in the other direc- Sections between Said pluriger and tw.o.shde tion 3 5 members operable when said plunger lS positioned 2. The invention defined in claim 1, wherein: at 9 angle on i l to reg'ster mter' said polygonal portion is a square portion extending felimg only for shfhng sadPlunger 0 cause from said one and substantially to the midportion F: j P f L lg of said guide pin to afford selective setting of said m en an emg opera 6 en plunger on Said guide pin at 0 spaced angles 40 plunger 18 positloned at another angle on its guide 3. The invention defined in claim 1, wherein said mof j to "i both mterfermg and F tion translating means including selective coupling and lfnerfermg sec nons to afford one F decoupling means comprises. tion of operat ng arm swing and switch operation a crank shaft attached to said operating arm; 9 filrecnon of .operafmg arm f cams mounted on Said crank Shaft; 7. The invention defined in claim 6, wherein said means providing interfering and non-interfering sections comprises:

a flange on said plunger having a notch;

a push plate secured to each said slide member, each push plate having tongues extending under and over said flange so that when said operating arm is swung, a first tongue moves said plunger to operate the switch and another tongue keeps said plunger from falling off when said operation head is detached;

and said plunger being positionable at angles where said notch provides clearance for said first tongue of one or the other or neither of said push plates.

8. The invention defined in claim 6, wherein said means mounting said guide pin to said operating head comprises:

a mounting plate seating into and secured to said operating head and having the polygonal end of said guide pin rigidly secured thereto;

the periphery of said plate being clamped between said operating head and said switch housing at the open end of the latter;

adjustment of its length thereby to adjust said plunger movement relative to said mating surface.

5. The invention defined in claim 4, wherein said means affording adjustment of the length of each said slide member comprises: 1

a screw whose head is accessible upon removal of said operating head subassembly to afford stepless adjustment of the length of said slide member and a pair of apertures in said mounting plate through which the respective slide members extend.

9. The invention defined in claim 8, wherein said means mounting said guide pin to said operating head further comprises:

a resilient diaphragm secured to each said slide member and to said mounting plate around the respective aperture in the latter to serve as a seal while affording sufficient movement of said slide member to operate the switch.

10. The invention defined in claim 6, wherein:

said polygonal end portion is a square end portion affording positioning of said plunger in any one of four different angular positions at 90 intervals and said slide members are spaced 180 apart.

11. The invention defined in claim 6, wherein each said slide member comprises:

a pair of sections biased apart to their full length by a compression spring and including means affording limited compression movement thereof to provide a resilient switch actuating force therethrough. 12. The invention defined in claim 11, wherein each said slide member further comprises:

an adjusting screw extending through said pair of sections so that one of said sections is biased by said compression spring against the head of said screw and the other section is threaded on said screw to afford stepless adjustment of the length of each said slide member by turning the adjusting screw @3 3 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,793,492 Dated February 19, 1974 Inventoflg) Eugene F. Duncan & Robert Pearson It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

, I Column 1, line 9, "inconvenient" should read inconvenience Column 1, line 64, after members" insert Column 2, line 1, "contact" should read switch Column 2, line 25, "if" should read is Column 2, line 58, "Figs. 2-6" should read Figs". 2-5 Column 2, line 59, "Fig. 2" should read Figs. 3 and 4 Column 3, line 28, should read after "24", shown in Fig. 5 Column 3, line 35, should read after "slide", member or Column 3, line 46, "listing" should read lifting Column 3, line 51, "Fig. 2 should read Figs. 2 and 3 Column 3., line 66, should read is clamped between the bushing 46 and the push plate 42 to form Q Column 4, line 16 "54a" should read 54b v a Column 4, line 22, "present" should read preset Column 4, line 23, "or" should read of Column 4,, line 29, "left" should read lift Column 4, line 59, "or" should read of Column 4, line 68, should read and the waster for compression of the peripheral bead of the seal Column 5, line 40, after "housing" continue as seen in Fig. l

Signed and sealed this 24th day of September 1974.

(SEAL) Attest':

MCCOY M. GIBSON JR. 0. MARSHALL DANN L Attesting Officer Commissioner of Patents J 

1. A limit switch comprising: a self-enclosed switch subassembly having an open end, and a self-enclosed operating head subassembly having a mating surface secured to said open end to close the latter and provide a limit switch allowing detachment of the operating head without any parts falling out; said switch subassembly comprising an enclosure, switch contacts within said enclosure and switch actuating means within said enclosure and accessible at the open end thereof for actuation by said operating head; and said operating head subassembly comprising: a housing; an external operating arm mounted on said housing and adapted to be moved in opposite directions to operate the switch; a fixed guide pin having a polygonal portion extending in from one end and a round portion extending in from the other end, and means mounting said guide pin at said one end so that its round end extends into the open end of said switch enclosure; a plunger having a bore complementary to said polygonal portion whereby said plunger is non-rotatably slidable on said guide pin to actuate said switch actuating means and said plunger being manually slidable further to said round portion upon removal of said operating head and rotated to another angle to select between bidirectional switch operation and by-pass in one direction; and motion translating means including selective coupling and decoupling means operable when said plunger is positioned on said guide pin at a given angle for rendering said coupling means effective to slide said plunger to cause switch operation when said external operating arm is moved in either direction, and being operable when said plunger is set on said guide pin at a different angle for rendering said coupling means effective to slide said plunger to cause switch operation when said external operating arm is moved in one direction and for renderiNg said de-coupling means effective to clear said plunger to afford by-pass when said external operating arm is moved in the other direction.
 2. The invention defined in claim 1, wherein: said polygonal portion is a square portion extending from said one end substantially to the midportion of said guide pin to afford selective setting of said plunger on said guide pin at 90* spaced angles.
 3. The invention defined in claim 1, wherein said motion translating means including selective coupling and decoupling means comprises: a crank shaft attached to said operating arm; cams mounted on said crank shaft; rockers mounted in said housing for actuation by said cams; a pair of slide members in said housing for actuation by said rockers; a flange on said plunger having a cutout at a predetermined angle; and a pair of push plates secured to the respective slide members and extending under said flange whereby both push plates slide said plunger at said given angle and one push plate passes freely through said cutout at said different angle for by-pass in one direction of operating arm movement.
 4. The invention defined in claim 3, wherein: each said slide member comprises means affording adjustment of its length thereby to adjust said plunger movement relative to said mating surface.
 5. The invention defined in claim 4, wherein said means affording adjustment of the length of each said slide member comprises: a screw whose head is accessible upon removal of said operating head subassembly to afford stepless adjustment of the length of said slide member thereby to preset the switch trip point at a desired operating arm angle.
 6. In a limit switch of the type having a switch housing open at one end and a switch within the housing, switch operating means comprising: switch actuating means in the switch housing and accessible from the open end thereof for actuating the switch; and an operating head attached to the open end of the switch housing for engaging said switch actuating means to operate the switch comprising: a switch operating arm adapted to be swung in opposite directions to operate the switch; a pair of slide members slidably mounted in said operating head for reciprocal movement; a return spring biasing said switch operating arm in its center off position from which it is adapted to be swung in opposite directions; means operable when said operating arm is swung in said opposite directions for moving the respective slide members; a fixed guide member having a polygonal end portion and means mounting it to said operating head and a round free end portion extending toward the switch housing; a plunger having a bore complementary to said polygonal end portion whereby it is slidably received on said guide member to be non-rotatably slidable thereon for switch operation and adapted to be manually slid further to said round portion and rotated to another angle; and means providing interfering and non-interfering sections between said plunger and the two slide members operable when said plunger is positioned at one angle on its guide member to register interfering sections only for sliding said plunger to cause switch operation when said operating arm is swung in either direction, and being operable when said plunger is positioned at another angle on its guide member to register both interfering and non-interfering sections to afford by-pass in one direction of operating arm swing and switch operation in the other direction of operating arm swing.
 7. The invention defined in claim 6, wherein said means providing interfering and non-interfering sections comprises: a flange on said plunger having a notch; a push plate secured to each said slide member, each push plate having tongues extending under and over said flange so that when said operating arm is swung, a first tongue moves said plunger to operate the switch and another tongue keeps said plunger from Falling off when said operation head is detached; and said plunger being positionable at angles where said notch provides clearance for said first tongue of one or the other or neither of said push plates.
 8. The invention defined in claim 6, wherein said means mounting said guide pin to said operating head comprises: a mounting plate seating into and secured to said operating head and having the polygonal end of said guide pin rigidly secured thereto; the periphery of said plate being clamped between said operating head and said switch housing at the open end of the latter; and a pair of apertures in said mounting plate through which the respective slide members extend.
 9. The invention defined in claim 8, wherein said means mounting said guide pin to said operating head further comprises: a resilient diaphragm secured to each said slide member and to said mounting plate around the respective aperture in the latter to serve as a seal while affording sufficient movement of said slide member to operate the switch.
 10. The invention defined in claim 6, wherein: said polygonal end portion is a square end portion affording positioning of said plunger in any one of four different angular positions at 90* intervals and said slide members are spaced 180* apart.
 11. The invention defined in claim 6, wherein each said slide member comprises: a pair of sections biased apart to their full length by a compression spring and including means affording limited compression movement thereof to provide a resilient switch actuating force therethrough.
 12. The invention defined in claim 11, wherein each said slide member further comprises: an adjusting screw extending through said pair of sections so that one of said sections is biased by said compression spring against the head of said screw and the other section is threaded on said screw to afford stepless adjustment of the length of each said slide member by turning the adjusting screw. 